Genotoxicity in the Environment (Eco-Genotoxicity)

Genotoxicity is a priority measurement for assessment and communication of genotoxic effects (DNA strand breaks) in the water matrix and the trophic levels of the ecosystem (Eco-Genotoxicity). Genotoxicity induction with single substances and surface water samples shows clearly the good sensitivity and reproducibility of the DNA-unwinding assay. The DNA alkaline unwinding assay detects levels of DNA fragmentation; the relative numbers of DNA strand breaks are described as the “-log F -value.” The results of DNA fragmentation in genotoxin-exposed cells of a RTG-2 cell line, the mussel Dreissena polymorpha, and fish larvae of the fish species Danio rerio are discussed. The early life stages of the fish species D. rerio show the significant high sensitivity and reproducibility of the DNA alkaline unwinding assay. As a reference method for the validation of genotoxicity pulsed-field gel electrophoresis (PFGE) was investigated. The LOEC (Lowest Observed Effect Concentration) of the genotoxin 4-nitroquinoline- N -Oxid (4-NQO) was 78 μg l⁻¹ for both test organisms, cell lines and fish larvae. Native surface water samples from representative stations on the River Rhine and the River Elbe significantly induced genotoxicity in the RTG-2 fish cell line and in fish larvae from D. rerio. An increased sensitivity was measured in D. rerio fish larvae 48 h after hatching during 3 h-exposure. The LOEC of the mussel D. polymorpha exposed in river water was less sensitive in the DNA alkaline unwinding assay: LOEC = 250 μg 1⁻¹ 4-NQO. In coastal waters the marine mussel Mytilus edulis is a good indicator organism for the detection of genotoxic effects and biotoxins. Beside immunotoxicity also genotoxic effects (DNA strand breaks) are found especially in UV-B (ultraviolet-B) exposed mussels (Luckas, B., J. Dahlmann, K.Erler, G. Gerdts, N. Wasmund, C. Hummert, P.-D. Hansen (2005) An Overview on Key Phytoplankton Toxins and their recent occurrence in North Sea and Baltic. Environmental Toxicology 20(1):1–17). To validate the influence of UV-B on exposed mussels (hepatopancreas and mussel hemocytes) UV-B exposure was investigated (Figs. 1 and 2) to induce and demonstrate eco-genotoxic effects in mussels and fish embryos. The fish eggs of the marine fish species Limanda limanda were experimentally exposed to UV-B radiation in a solar radiation simulator onboard the research vessel RV Walther Herwig III. The experimental design attempted to simulate present and future conditions in the context of eco-genotoxicity and increased UV-B exposure due to northern hemisphere ozone loss. The impact of low dosages of UV-B indicates an important genotoxic and ecological threat concerning ecosystem integrity status at the population level. In our experiments embryos of L. limanda taken from sites located along a gradient of chemical stress in the German Bight were exposed to solar ultraviolet-B light and allowed to recover for a defined period. The involved research groups from different disciplines and research organizations showed a significant time and dosage-dependent influence of UV-B radiation on mortality and sublethal eco-genotoxic effects (DNA damage in the environment). Our hypothesis was that there might be an interaction between exposure to chemical contaminants and the ability of embryos to recover from UV-induced genotoxic effects by repairment.